The invention relates to an optical card capable of optical information recording, and technology for producing it.
An optical card has been known as a memory card incorporating an optical recording zone, i.e., an optical information recording zone, in a plastic card. FIG. 1 shows an example of a WORM (write-once/read-many) type optical card. In an optical recording zone 2 of this optical card 1, track guides 4 and information recording pits 5, each composed of a low reflectance area, are formed as preformats along with high reflectance areas. Among optical cards of this type is an optical card whose low reflectance areas are composed of light scattering surface roughened portions. Such an optical card has been proposed as a product using an optical recording medium whose manufacturing process is relatively simple, whose material is not restricted to a particular optical recording material, and whose production cost is low enough to be suitable for mass reproduction on a commercial scale (see, for example, Japanese Patent Publication No. 64141/95). The production of this optical card begins with the preparation of a surface-roughened original plate having low reflectance areas surface roughened according to an information record pattern. The resulting original plate is duplicated and transferred to mass produce the optical card having a rough surface information record pattern.
The steps for its manufacturing process will be described with reference to the accompanying drawings.
At a first stage, a positive photoresist is uniformly coated on a transparent substrate 11 (a 400 .mu.m thick acrylic plate) to a thickness of 0.5 .mu.m by means of a rotary photoresist coater to form a photoresist layer 12, as shown in FIG. 2A. At a second stage as shown in FIG. 2B, a photomask 13 formed in accordance with an information record pattern is superimposed on the photoresist layer 12 using a mask aligner, and then initial exposure (patterning exposure) is performed. At a third stage as shown in FIG. 2C, a glass sheet 14 roughened on one surface in a finely uneven form (average roughness 0.3 .mu.m, #3000 abrasive glass) is used, and exposure is performed again (surface roughening exposure). After exposure, the photoresist layer 12 is developed at a fourth stage. Thus, as shown in FIG. 2D, the pattern of the photomask 13 is transferred onto the transparent substrate 11, with the exposed areas of the photoresist being dissolved and the unexposed areas remaining. By this measure, the surface roughened photoresist layer 12 is formed as guide tracks, for example, with a width of about 2.5 pm and a pitch of about 15 .mu.m.
Then, an optical recording medium having an information record pattern composed of low reflectance areas roughened on the surface (a medium as shown in FIG. 2D) is used as a surface roughened original plate 15. From this surface roughened original plate 15, a mother mask is duplicated using a molding press. Specifically, as shown in FIG. 3A, the surface roughened original plate 15 is superimposed on a transparent substrate 21 (an acrylic plate 12 mm in thickness) via an impression material 22 comprising a molding compound of an ionizing radiation curable resin or a thermosetting resin. The combination is pressed, and then the surface roughened original plate 15 is stripped to duplicate a pattern on the transparent substrate 21 side, thus forming a mother mask 23.
Then, the mother mask 23 is used as a duplicating original plate for mass duplication, and impression using it is performed to duplicate an optical recording medium on the back of a substrate serving as a transparent protective layer of an optical card. In detail, as shown in FIG. 4A, a molding resin 33 is interposed between the back of a transparent protective layer 32 having a surface hardening layer 31 and the pattern surface of a mother mask 23. The assembly is pressed by a pressing machine to undergo hardening. Then, as shown in FIG. 4B, the transparent protective layer 32 and the mother mask 23 are released from the mold to duplicate a pattern on the transparent protective layer 32 side. In this manner, high reflectance areas 33a and low reflectance areas 33b are formed on the duplicating resin 33 to serve as an optically transparent substrate for an optical card.
Then, as shown in FIG. 5, an optical recording material layer 34 of, say, the intermediate oxide of Te, is laminated to cover the high reflectance areas 33a and low reflectance areas 33b in the optically transparent substrate composed of the duplicating resin 33.
Separately from the foregoing series of steps, a card substrate 35 as shown in FIG. 6 is prepared. This card substrate is formed by applying a print layer 36 to one surface of a core sheet 35b comprising translucent polyvinyl chloride, and bonding overlay sheets 35a, 35c comprising transparent polyvinyl chloride to both surfaces of the core sheet 35b.
Then, the card substrate 35 is adhesion laminated to the substrate having the optical recording material layer 34 via an adhesive layer 37 comprising urethane resin, as shown in FIG. 7. The so prepared master is punched into a card form to produce an optical card as illustrated in FIG. 1.
The aforementioned production of a conventional surface roughened original plate posed the problem that the resulting roughened surface contained defective areas because of the processing method during production, the limits of the properties of the materials used, and slight changes in the manufacturing conditions. In extreme cases, the resulting original plate partially had no sufficiently low reflectance. Optical cards duplicated from such an original plate were not entirely satisfactory in the contrast of the preformat portions.